A Portable Magnetometer for Magnetic Measurements of Meter‐Sized Meteorites

Elise Clavé, Clara Maurel, Eduardo A. Lima, Jay Shah, Elias N. Mansbach, Minoru Uehara, Benjamin P. Weiss

Geochemistry, Geophysics, Geosystems
First published: 02 October 2020


“Meteorites contain records of past magnetic fields experienced on their parent bodies in the form of natural remanent magnetization (NRM). A key property of meteorite magnetization, which provides information about its origin, is the scale of spatial variations of the remanent magnetization. In particular, understanding how the mean remanent magnetization varies from the scale of meteorites to the global scale of their parent bodies would aid in the interpretation of spacecraft magnetometry data. However, the vast majority of meteorite samples whose remanent magnetization have been measured have sizes < 10 cm due to the limited size range accommodated by the instruments. To address this limitation, we developed a portable magnetometer array that enables remanence measurements of meter‐size meteorites in a non‐magnetically shielded environment. The instrument measures both NRM and induced magnetization through the use of two orthogonal square Helmholtz coil pairs that compensate the vertical and horizontal components of the background magnetic field. An array of four magnetometers mounted on a movable aluminum rail measures the magnetic field at multiple locations around the sample. The instrument is transportable and can be adapted to different sample sizes. After distinguishing the induced component from the remanent component of the sample’s total field, the remanence can be estimated from a multipole field inversion combined with non‐linear least squares method. We validated the instrument and data processing on a magnet of known magnetic moment and, as an example, used the system to measure the NRM of a meter‐sized iron meteorite.”

” Plain Language Summary

Meteorites are remnant fragments of planetary bodies. Their physical properties reflect the environment and internal activity prevailing on these bodies. In particular, some meteorites preserve records of past magnetic fields experienced on their parent asteroids in the form of natural remanent magnetization. This remanence can be probed by spacecraft magnetometers to infer the intensity and direction of ancient magnetizing fields. However, it is unclear how to connect global scale measurements of planetary magnetization to that of meteorites measured in the laboratory. A major limitation is that the scaling of meteorite magnetization with size is largely unknown. Establishing such scaling requires measuring the remanent magnetizations of larger and larger meteorites. However, nearly all meteorites previously analyzed were typically smaller than ∼10 cm in diameter owing to the size and portability of the instruments. To facilitate the measurements of larger meteorites, we designed and built a portable instrument that enables measurements of the remanent and induced magnetizations of meter‐size meteorites at their storage location. We first validated the instrument performance against a sample of known magnetic moment and then used it to measure a large meteorite.”